Centrifuge construction

ABSTRACT

A rotor is mounted for rotation about a first axis, and a screen drum is mounted on the rotor for rotation about a second axis parallel to but laterally offset from the first axis. A conveying screw is mounted in the screen drum for rotation jointly with the rotor about the first axis and it has screw flights which extend close to an inner circumferential surface of the screen drum. A single drive rotates the screen drum at a first circumferential speed, and rotates the rotor and conveying screw at a different second circumferential speed, so that the screen drum on the one hand and the rotor and conveying screw on the other hand perform a relative rotation. An admitting arrangement admits a liquidcontaining mass into the screen drum. the liquid escapes from the screen drum during centrifuging and the centrifuged material forms on the inner circumferential surface of the screen drum a layer which, due to the difference between the first and second speeds, moves incrementally towards the conveying screw which engages it and removes it from the screen drum.

nited States Patent 11 1 Steprath Dec. 16, 1975 [73] Assignee:Maschinenfabrik Buckau R. Wolf Aktiengesellschaft, Grevenbroich,

Germany [22] Filed: Feb. 1, 1974 [21] Appl. No: 438,606 [30] ForeignApplication Priority Data Feb. 3, 1973 Germany ..2305326 [52] US. Cl.127/19; 210/380; 233/7;

233/22; 233/25 [5i] Int. Cl. B04b 5/00; B04b 9/08; Cl3f H06 [58] Fieldof Search 127/19, 56; 233/3, 7, 22, 233/25; 210/380 PrimaryExaminerMorris O. Wolk Assistant Examiner-Sidney Marantz Attorney,Agent, or Firm-Michael S. Striker 5 7] ABSTRACT A rotor is mounted forrotation about a first axis, and a screen drum is mounted on the rotorfor rotation about a second axis parallel to but laterally offset fromthe first axis. A conveying screw is mounted in the screen drum forrotation jointly with the rotor about the first axis and it has screwflights which extend close to an inner circumferential surface of thescreen drum. A single drive rotates the screen drum at a firstcircumferential speed, and rotates the rotor and conveying screw at adifferent second circumferential speed, so that the screen drum on theone hand and the rotor and conveying screw on the other hand per- [56]References cued form a relative rotation. An admitting arrangementUNITED STATES PATENTS admits a liquid-containing mass into the screendrum. 1,146,269 7/1915 Mauss 233/25 X the liquid escapes from the screendrum during centri- 1,339,272 5/1920 Mauss .1 233/25 fuging and thecentrifuged material forms on the inner QUiI'OZ 1 v. circumferentialurface of the creen drum a layer 2,883,054 4/1959 'f 127/19 X which, dueto the difference between the first and secgggi E 6 0nd speeds, movesincrementally towards the convey- 10/1966 Rotel 210/380 X mg screw WhlChengages 1t and removes it from the 3,402,821 9/1968 Peck 210/380 xScreen drum- 3,6'27,l38 12/1971 Peck 1 233/22 X 3,718,220 2/1973 Titus233/22 X 10 Claims, 2 Drawing Figures U.S. Patent Dec. 16, 1975 Sheet 1of2 3,926,661

FIG.

US. Patent Dec. 16, 1975 Sheet20f2 3,926,661

CENTRIFUGE CONSTRUCTION BACKGROUND OF THE INVENTION The presentinvention relates to a centrifuge construction and more particularly toa continuously operating centrifuge which is especially but notexclusively suitable for the production of sugar.

Continuous centrifuges are already well known, including in the field ofsugar production. It is known to provide centrifuges of this generaltype for use where differential centrifugal forces are required.Generally speaking, however, centrifuges of the prior art which providefor differential centrifugal force acting upon the material beingcentrifuged, are not suitable for the centrifuging of finished sugar orthe like, because in operation the sugar crystals impinge at high speedagainst a wall of the drum which causes them to crack and become blind.This latter term refers to a condition in which the sugar no longer hascrystalline appearance, and thus lacks the optical appeal associatedwith sugar. This makes sugar produced in this manner very difficult tosell.

SUMMARY OF THE INVENTION It is, accordingly, a general object of thepresent invention to provide a novel centrifuge construction whichavoids the disadvantages of the prior art.

More particularly, it is an object of the invention to provide acontinuously operating centrifuge which can be used for centrifuging offinished sugar or analogous products, and which reliably precludes thepossibility that the centrifuged crystals might be flung against a wallduring operation of the centrifuge, or might even move only along thiswall of the centrifuge drum during the centrifuging operation.

An additional object of the invention is to provide such an improvedcentrifuge construction in which the centrifuged crystals are dischargedfrom the centrifuge drum in a region of relatively small accelerationand travel speed.

In keeping with the above objects, and with others which will becomeapparent hereafter, one feature of the invention resides, in acentrifuge, in a combination which comprises a rotor mounted forrotation about a first axis, and a screen drum mounted on the rotor forrotation about a second axis parallel to but laterally offset from thefirst axis. A conveying screw is mounted in the screen drum for rotationjointly with the rotor about the first axis, and the conveying screw hasscrew flights which extend close to an inner circumferential surface ofthe screen drum.

Drive means is provided for rotating the screen drum at a firstcircumferential speed, and for rotating the rotor and conveying screw ata different second circumferential speed. Admitting means admits aliquidcontaining mass into the screen drum so that during centrifugingthe liquid can escape from the latter. The retained centrifuged materialforms on the inner circumferential surface of the screen drum a layerwhich, due to the difference between the first and second speeds and thethus obtained relative angular movements of the screen drum andconveying screw, moves incrementally towards the conveying screw forengagement by the same and conveyance out of the screen drum.

The drive means may utilize a single drive motor which, since it impartsdifferent angular velocities to the screen drum on the one hand, and therotor and conveying screw on the other hand, causes not only rotation ofthe screen drum and rotor with the conveying screw in one and the samedirection, but also causes a superimposed relative angular movementbetween the screen drum and the rotor with the conveying screw on theother hand. The layer which forms on the inside surface of the screendrum, and from which liquid has escaped due to the centrifugal force,travels incrementally together with the wall of the screen drum awayfrom the axis of the main rotation, that is it moves into zones where itis subjected to higher centrifugal acceleration and where further liquidthus is removed from it. As this incremental travel continues, the nowlargely liquid-free material, for instance sugar crystals, approachesthe main axis of rotation again, to finally reach the vicinity of theconveying screw which en gages increments of the layer and removes themfrom the conveying drum. During the entire operation the crystals orsimilar material remain in position on the inner circumferential wall ofthe screen drum and do not perform any movement relative to the latter.The discharge of the centrifuged material takes place in a region of lowacceleration and therefore in a zone of low mass forces.

The centrifuge construction according to the present invention has theadvantage, by comparison to the prior art, that no fracturing orbreaking-down of the crystal or other centrifuged material takes placeon the inner circumferential surface of the screen drum, due to impactor movement relative to this surface, and that at the time of dischargethe centrifuged crystals are subjected to almost no impact forces, sothat the disadvantages resulting in the prior art in the formation of,for instance, blind sugar, are avoided.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best undertood from the following description of specific embodimentswhen read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS:

FIG. 1 is an axial section through a centrifuge according to the presentinvention; and

FIG. 2 is a section taken on line II-II of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS:

Referring now to FIGS. 1 and 2, wherein one exemplary embodiment of theinvention is illustrated, the housing of the novel centrifuge will beseen to be designated with reference numeral 1. Mounted in the housing1, by means of axially spaced antifriction bearings 2 and 3, is a rotor4 which is composed of two axially spaced disk members 5 and 6. Thesehave eccentrically arranged circular recesses 7 and 8 provided in theirinwardly facing surfaces, that is in those surfaces which face oneanother in axial direction. The members 5 and 6 are also provided withcentral bores through which a hollow shaft 9 extends on which themembers 5 and 6 are fixed, for instance by means of non-illustratedflanges, by shrink fitting or the like.

As FIG. 2 shows most clearly, the hollow shaft 9 is provided with anaxially extending slotted opening 10 through which the centrifugedcrystals or similar material can enter into its interior. The length ofthe opening corresponds to the length of the screen drum 16. One edge 11bounding the opening 10 engages or is located directly proximal to theinner circumferential surface of the screen drum 16 and is configuratedas a scraper or doctor blade which engages beneath the layer 35 ofcentrifuged material (see FIG. 2) to lift it off the innercircumferential surface of the screen drum 16 and guide it intoengagement with the conveying screw 23 which extends through the hollowshaft 9.

It is clear that the recesses 7 and 8 are provided eccentrically on themembers 5 and 6, as previously pointed out; diametrally opposite thelocation of the recesses 7 and 8 the members 5 and 6 have portions 12and 13 which are configurated as counterweights, that is which aresuitably massive and heavy to act as counterweights. Thesecounterweights may, incidentally, be arranged to cooperate in knownmanner with an arrangement (known per se) for automatic compensating ofimbalances. (See DT-PS 2 140 006 or US. Pat. Application Ser. No.279,170).

The recess 7 accommodates an anti-friction bearing 14, and the recess 8similarly accommodates an antifriction bearing 15. The screen drum 16 ismounted for rotation in these bearings 14 and 15 and is composed of twoflat annular members 17 and 18 which are connected by a circumferentialscreen wall 19 so that with the latter they form the screen drum 16.Bearing rings 20 and 21 are provided by means of which the drum 16 isjournaled in the anti-friction bearings 14 and 15, respectively.

In the region of the bearing ring 20 the screen drum 16 is also providedwith an internal ring gear 22 the teeth of which mesh with the teeth ofa pinion which is fixedly mounted on the shaft 24 of the conveying screw23. Also mounted on this shaft 24 is a belt pulley 26 by means of whichthe shaft 24 is driven in rotation so that the screw flights of thescrew 23 which are mounted on the shaft 24 and fixed to the same, rotatewith the shaft. In the region of the annulus 18 the flights of the screw23 are interrupted at 23a.

The shaft 9 is formed at its left-hand end (with respect to FIG. 1) witha collecting chamber 36, and it is further formed with a passage 37 theopposite ends of which communicate with the chamber 36 and the interiorof screen drum 16, respectively. A conduit 39 extends into an open endof the chamber 36 and the material to be centrifuged is admitted intothis chamber via the conduit 39.

At the opposite axial end from the chamber 36, the shaft 9 is formedwith a further chamber 38 through which the centrifuged material is tobe expelled by the screw 23.

A second belt pulley 27 is fixedly mounted on the shaft 9 in the regionof the chamber 36; the diameter of the belt pulley 27 is somewhat largerthan that of the belt pulley 26. Both pulleys 26 and 27 are driven, viabelts 28 and 29, respectively, from an output pulley 30 of a commondrive motor 31. It is evident that the diameter differential of the beltpulleys 26 and 27 will cause the shaft 24 to rotate somewhat faster thanthe shaft 9.

FIG. 2 shows that the axis of rotation of the shaft 24 of the conveyingscrew 23 coincides with the main axis of rotation 33 of the rotor 4. Theconveying screw 23 is so mounted that its outer diameter intersects theinner diameter of the screen drum 16 and a tangent, that is thearrangement is such that the screw 23 can engage and remove the layer35' of centrifuged material which has formed on the innercircumferential surface of the screen drum 16. The axis of rotation ofthe screen drum 16 is identified with reference numeral 34 in FIG. 2,and electro-motor 31 is mounted in suitable manner, for instance bymeans of a socket 32 or the like, on the centrifuge housing 1.

In operation, the material to be centrifuged is admitted via the conduit39 into the chamber 36, and travels from there through the passage 37into the interior of the screen drum 16. It is discharged into thescreen drum 16 at the location A shown in FIG. 2, with the result thatin this region a layer 35 of the material will form on the innercircumferential surface of the screen drum 16. Because of the high-speedrotation of the rotor 4 and the consequent centrifugal action, liquid iscentrifugally removed from the layer 35, that is the liquid passes outthrough the screen openings of the screen drum 16.

During the rotation of the rotor 4 the screen drum 16 performs arelative angular movement, that is a movement with respect to the rotor4 at the same time as the screen drum also rotates with the rotor 4about the axis 33. The result of this relative angular movement is thatthe material which has been admitted at A in FIG. 2 will travel slowlyand incrementally in clockwise direction towards the opening 10 of theshaft 9. Evidently, the dwell time of the material in the screen drum16, that is the time required for any increment of the layer 35 totravel from the location A to the opening 10, can be varied by varyingthe speed at which the screen drum 16 rotates with reference to therotor 4. Such a variation can be obtained by changing the diameter ofthe pulley 27 with respect to that of the pulley 26, and this in turncan be done by utilizing variable sheaves or the like.

In any case, as soon as the increments 35' of the layer 35 that is thenow centrifuged crystals or the like, reach the vicinity of the opening10, and come in contact with the edge 1 1 thereof, they are lifted offthe inner circumferential surface of the screen drum 16 and directedtowards the conveyor screw 35 which engages the material and ejects itaxially from the screen clrum 16, or rather from the hollow shaft 9which extends through the screen drum 16, through the chamber 38.

It is pointed out that although in the illustrated embodiment the axesof rotation of the rotor 4 and the screen drum 16 have been shown to behorizontal, it is well within the concept and intent of the presentinvention to have these axes be either vertical or substantiallyvertical, without in any sense departing from the concepts of theinvention.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied in acentrifuge, it is not intended to be limited to the details shown, sincevarious modifications and structural changes may be made withoutdeparting in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset 'forth in the appended claims.

1. In a centrifuge, a combination comprising a rotor mounted forrotation about a first axis; a screen drum mounted on said rotor forrotation about a second axis parallel to but laterally offset from saidfirst axis; a conveying screw mounted in said screen drum for rotationjointly with said rotor about said first axis, said conveying screwhaving screw flights which extend close to an inner circumferentialsurface of said screen drum; drive means for rotating said screen drumat a first circumferential speed, and for rotating said rotor and conveying screw at a different second circumferential speed; and admittingmeans for admitting a liquid-containing mass into said screen drum, sothat during centrifuging the liquid can escape from the latter whereasthe retained centrifuged material forms on said inner circumferentialsurface which, due to the difference between said first and secondspeeds, moves incrementally towards said conveying screw for engagementby the same and conveyance out of said screen drum.

2. A combination as defined in claim 1, wherein said rotor comprises ahollow shaft extending eccentrically through said screen drum andinternally accommodating said conveyor screw, and a pair of disk membersmounted on said shaft axially spaced from one another and fixed to saidshaft for rotation therewith, said shaft having an axially extendingslot in its circumferential wall through which said retained centrifugedmaterial of said layer enters.

3. A combination as defined in claim 2, wherein said disk members eachhave one radial side where said screen drum is located, and adiametrically opposite radial side which is configurated as acounterweight.

4. A combination as defined in claim 3; and further comprising meanscooperating with said counterweights and operative for effectingautomatic correction of imbalances of said rotor.

5. A combination as defined in claim 2, wherein said slot is bounded byan edge portion configurated as a scraper for scraping increments ofsaid layer from said inner circumferential surface of said screen drum.

6. A combination as defined in claim 2, wherein said screen drum isprovided with an internal gear surrounding said second axis; and whereinsaid conveying screw comprises a shaft member extending through saidscreen drum and ring gear, and a pinion fixedly mounted on said shaftmember and meshing with said ring gear.

7. A combination as defined in claim 2, wherein said hollow shaftcomprises one end portion projecting axially outwardly past one of said.disk members and being formed with an inlet chamber, and another endportion projecting axially outwardly past the other of said disk membersand being formed with an outlet chamber into which said conveying screwextends.

8. A combination as defined in claim 7, wherein said hollow shaft isfurther provided with a passage having one open end communicating withsaid inlet chamber, and another open end communicating with the interiorof said screen drum.

9. A combination as defined in claim 8, wherein said admitting meanscommunicates with said inlet chamber for admitting into the same saidmass which travels via said passage into said screen drum.

10. A combination as defined in claim 1, wherein said drive meanscomprises a single drive motor.

1. IN A CENTRIFUGE, A COMBINATION COMPRISING A ROTOR MOUNTED FORROTATION ABOUT A FIRST AXIS; A SCREEN DRUM MOUNTED ON SAID ROTOR FORROTATION ABOUT A SECOND AXIS PARALLEL TO BUT LATERALLY OFFSET FROM SAIDFIRST AXIS; A CONVEYING SCREW MOUNTED IN SAID SCREEN DRUM FOR ROTATIONJOINTLY WITH SAID ROTOR ABOUT SAID FIRST AXIS, SAID CONVEYING SCREWHAVING SCREW FLIGHTS WHICH EXTEND CLOSE TO AN INNER CIRCUMFERENTIALSURFACE OF SAID SCREEN DRUM; DRIVE MEANS FOR ROTATING SAID SCREEN DRUMAT A FIRST CIRCUMFERENTIAL SPEED, AND FOR ROTATING SAID ROTOR ANDCONVEYING SCREW AT A DIFFERENT SECOND CIRCUMFERENTIAL SPEED; ANDADMITTING MEANS FOR ADMITTING A LIQUID-CONTAINING MASS INTO SAID SCREENDRUM, SO THAT DURING CENTRIFUGING THE LIQUID CAN ESCAPE FROM THE LATTERWHEREAS THE RETAINED CENTRIFUGED MATERIAL FORMS ON SAID INNERCIRCUMFERENTIAL SURFACE WHICH, DUE TO THE DIFFERENCE BETWEEN SAID FIRSTAND SECOND SPEEDS, MOVES INCREMENTALLY TOWARDS SAID CONVEYING SCREW FORENGAGEMENT BY THE SAME AND CONVEYANCE OUT OF SAID SCREEN DRUM.
 2. Acombination as defined in claim 1, wherein said rotor comprises a hollowshaft extending eccentrically through said screen drum and internallyaccommodating said conveyor screw, and a pair of disk members mounted onsaid shaft axially spaced from one another and fixed to said shaft forrotation therewith, said shaft having an axially extending slot in itscircumferential wall through which said retained centrifuged material ofsaid layer enters.
 3. A combination as defined in claim 2, wherein saiddisk members each have one radial side where said screen drum islocated, and a diametrically opposite radial side which is configuratedas a counterweight.
 4. A combination as defined in claim 3; and furthercomprising means cooperating with said counterweights and operative foreffecting automatic correction of imbalances of said rotor.
 5. Acombination as defined in claim 2, wherein said slot is bounded by anedge portion configurated as a scraper for scraping increments of saidlayer from said inner circumferential surface of said screen drum.
 6. Acombination as defined in claim 2, wherein said screen drum is providedwith an internal gear surrounding said second axis; and wherein saidconveying screw comprises a shaft member extending through said screendrum and ring gear, and a pinion fixedly mounted on said shaft memberand meshing with said ring gear.
 7. A combination as defined in claim 2,wherein said hollow shaft comprises one end portion projecting axiallyoutwardly past one of said disk members and being formed with an inletchamber, and another end portion projecting axially outwardly past theother of said disk members and being formed with an outlet chamber intowhich said conveying screw extends.
 8. A combination as defined in claim7, wherein said hollow shaft is further provided with a passage havingone open end communicating with said inlet chamber, and another open endcommunicating with the interior of said screen drum.
 9. A combination asdefined in claim 8, wherein said admitting means communicates with saidinlet chamber for admitting into the same said mass which travels viasaid passage into said screen drum.
 10. A combination as defined inclaim 1, wherein said drive means comprises a single drive motor.